A new service that offers patients a private same-day appointment with an NHS GP could be rolled out nationally.
The Uber-style service Doctaly charges patients between £39.99 and £49.99 for an appointment during office hours, enabling patients to skip NHS queues to see a doctor.
The cost rises to £69.99 for appointments out of hours, such as before 9am and after 6pm on weekdays and during the weekend
The Doctaly service has been piloted in north London at 10 practices in Barnet and Enfield and has proved so successful that its founders now plan to roll it out, with national coverage expected by 2018.
Around 50 GPs are currently signed up to the scheme.
Patients log on to the Doctaly website to book an appointment with an NHS GP at a time and location that is convenient to them.
They cannot see their own GP or one registered at their practice, but can choose another doctor working nearby.
Consultations are for 15 minutes - around five minutes longer than a standard NHS one.
Company founder Ben Teichman told Pulse magazine that the service was not about queue-jumping and could stop patients unnecessarily going to A&E.
Critics argue that Doctaly will create a two-tier health system, and is a step closer towards privatising the NHS.
Mr Teichman, who set up the company with his GP friend Dr Dinesh Silva, said: "Doctaly is essentially a hybrid service between the NHS and existing private practice making private appointments more affordable, thereby opening them up to a wider audience.
"It is not about queue-jumping. Quite the opposite in fact. It should help drive queues down in surgeries and also take traffic away from A&E. An A&E appointment can cost the NHS £150 and if access wasn't an issue, many of these patients could have been successfully treated by a GP."
He said the service was a "lucrative and convenient alternative" for part-time GPs, and even full-time GPs who may "want to do a few appointments on their admin day if they've got time".
The Doctaly website pledges to offer GPs who "provide top quality medical care seven days a week".
It adds: "You have access to a number of private medical services including women's health, child health, men's health, private medicals, sexual health screening and private STD testing.
"If you require medication, your GP will provide you with a private prescription which can be used at any UK pharmacy."
The service is similar to Uber in that it does not employ GPs itself but matches willing doctors working in their own surgeries with patients who can pay.
Dr Jackie Applebee, chairwoman of Tower Hamlets local medical committee and Doctors in Unite representative on the British Medical Association's GPs committee, said Doctaly was "very worrying" and would "further destabilise general practice".
She told Pulse: "This is not the answer to the crisis in general practice. I acknowledge that access is a problem, but the fault for this lies at the door of the Government who have dis-invested in general practice for years so that we now have an unprecedented workforce crisis.
"This sort of service is the slippery slope towards privatisation of the NHS. It introduces the principle of topping up NHS services with purchased services if one has the disposal income. If the more affluent begin to do this in significant numbers it is only a small step to an insurance-based health service."
Dr Richard Vautrey, deputy chairman of the BMA's GP committee, said: "Patients want and deserve a properly-funded NHS GP service, based on the registered list, so they can get appropriate timely access to their local GP and that practices have the resources and capacity to offer this.
"While patients can access and pay for private GPs or consultants, the risk is a more fragmented service and patients having remote consultations with doctors they don't know and who won't have full access to their NHS medical record."